As is well known, fluid dynamic bearing devices have features in their high speed rotation, high rotational accuracy, quietness, and the like. Thus, the fluid dynamic bearing devices are suitably used as bearing devices for motors to be mounted to various electrical apparatus such as information apparatus, and more specifically, as bearing devices for spindle motors to be built in disk drives of HDDs and the like, for fan motors to be built in PCs and the like, or for polygon scanner motors to be built in laser beam printers (LBPs).
The fluid dynamic bearing device includes radial bearing portions for supporting a member on a rotary side in a radial direction, and thrust bearing portions for supporting the member on the rotary side in thrust directions. In recent years, in order to effectively obtain the above-mentioned features, the radial bearing portions and the thrust bearing portions have each been formed of a fluid dynamic bearing in many cases. There have been proposed various fluid dynamic bearing devices of this type. For example, Patent Literature 1 discloses, in FIG. 2, a fluid dynamic bearing device including a sintered-metal bearing member on the rotary side, and a housing on the stationary side, which receives the bearing member on its inner periphery. Radial bearing gaps of radial bearing portions are formed between an outer peripheral surface of the bearing member and an inner peripheral surface of the housing. Further, in this fluid dynamic bearing device, thrust bearing gaps of thrust bearing portions are formed respectively on one end surface and another end surface of the bearing member.
When the configuration of Patent Literature 1 is employed, the support areas in the radial bearing portions can be set to be larger than those in a configuration in which the radial bearing gaps of the radial bearing portions are formed between an outer peripheral surface of a shaft member and an inner peripheral surface of the bearing member fixed to the inner periphery of the housing (for example, Patent Literature 2). In addition, due to a centrifugal force to be applied to lubricating oil along with rotation of the bearing member, the radial bearing gaps can be filled with an ample amount of the lubricating oil. Thus, there is an advantage in that supportability of the radial bearing portions can be enhanced and stably maintained.